Whitehead torsion V (Ex)
(Difference between revisions)
m |
m |
||
Line 3: | Line 3: | ||
# Show that the operations (1)-(5) from {{citeD|Lück2001|Section 1.4}} used in the definition of the Whitehead group in fact yield equivalence classes of invertible matrices of arbitrary size. | # Show that the operations (1)-(5) from {{citeD|Lück2001|Section 1.4}} used in the definition of the Whitehead group in fact yield equivalence classes of invertible matrices of arbitrary size. | ||
# Show that addition is well-defined in the Whitehead group via | # Show that addition is well-defined in the Whitehead group via | ||
− | $$ [A] + [B] = \left [\begin{array}{cc} A & 0 \\ 0 & B \end{array} \right] = [ | + | $$ [A] + [B] = \left [\begin{array}{cc} A & 0 \\ 0 & B \end{array} \right] = [A \cdot (B \oplus \text{Id}_{n-m})].$$ |
− | Here $A$ is an $n \times n$ matrix, $B$ is an $m \times m$ matrix with $n \geq m$, $O$ denotes the zero $n \times m$ and $m \times n$ matricies and $\cdot$ denotes matrix multiplication. | + | Here $A$ and $B$ are invertible matricies over the group ring $\Zz[\pi]$, $A$ is an $n \times n$ matrix, $B$ is an $m \times m$ matrix with $n \geq m$, $O$ denotes the zero $n \times m$ and $m \times n$ matricies and $\cdot$ denotes matrix multiplication. |
# Show that $Wh(e)$ is trivial. | # Show that $Wh(e)$ is trivial. | ||
{{endthm}} | {{endthm}} |
Revision as of 12:17, 26 March 2012
Exercise 0.1.
- Show that the operations (1)-(5) from [Lück2001, Section 1.4] used in the definition of the Whitehead group in fact yield equivalence classes of invertible matrices of arbitrary size.
- Show that addition is well-defined in the Whitehead group via
Here and are invertible matricies over the group ring , is an matrix, is an matrix with , denotes the zero and matricies and denotes matrix multiplication.
- Show that is trivial.
The exercises and hints on this page were sent by Alex Koenen and Arkadi Schelling.